The present invention generally relates to gas turbine combustors and, more particularly, is concerned with a fuel nozzle centering device and method for gas turbine combustors.
As depicted in FIGS. 1 to 3, a prior art gas turbine generally includes a combustor 10 having a main combustion chamber 12 and one or more burners 14 attached to the main combustion chamber 12. Compressed air enters the burner 14 from the left and flows to the right through the combustor 10. Air is provided by a compressor (not shown) and may be reversed flowed over the combustor 10 before entering the burner 14. While only one burner 14 is shown for clarity of illustration, a plurality of burners 14 is preferably used. Typically, five or six burners are arranged in a circular array on the main combustion chamber 12.
The main combustion chamber 12 includes a liner 16 having an upstream end 16A and an opening 18 defined in the liner 16 by an annular collar 20 attached to the upstream end 16A of the liner 16. The burner 14 typically includes a cylindrical flow tube (not shown) and a fuel nozzle 22 concentrically disposed within the flow tube. The fuel nozzle 22 includes a cylindrical hub 24, an annular flange 26 interconnected with and extending circumferentially around the hub 24, and a tip 28 interconnected with and disposed downstream from the hub 24. The fuel nozzle flange 26 defines a plurality of through-holes 30 which are circumferentially spaced apart from one another. The combustor 10 also includes a cover 32 and a plurality of bolts 34. The cover 32 has a plurality of holes 36 defined therein being alignable with the holes 30 of the fuel nozzle flange 26. The bolts 34 are inserted through the through-holes 30 of the fuel nozzle flange 26 and into the holes 36 of the cover 34 and thereby removably secure the fuel nozzle flange 26 and combustor cover 32 to one another. The fuel nozzle tip 28 has an outer periphery 38 where it is assembled into the liner collar 20.
Due to many stack-up tolerances involved in assembling fuel nozzles of burners into the liner of the main combustion chamber, fuel nozzle misalignment is commonplace and causes a redundancy in liner head end support by sharing the support load between the fuel nozzle and liner stops (not shown). Operational experience and analysis has shown that this type of system creates an environment where dynamics are higher and part wear is increased. In the current system, fuel nozzles are assembled into liner collars through a complex assembly of parts. To allow for the stack-up of tolerances, clearances between the parts, especially at the bolts, is necessary. Because of this, misalignment of the fuel nozzle often occurs.
Various devices and methods have been developed over the years toward providing a solution of the aforementioned problem of misalignment of the fuel nozzle. The primary devices and methods employed in the industry have been the use of floating liner collars 40, as shown in FIG. 2, and of a body bound arrangement, as shown in FIG. 3. The floating liner collar 40 makes up for fuel nozzle misalignment by allowing the liner collar to "float" through a predetermined clearance. While this device and method has been somewhat satisfactory, it is expensive due to its complexity and has been prone to create additional wear problems, particularly in the liner collar itself. The body bound arrangement usually replaces three of the bolt through-holes with tapered bolts 42 that attempt to center the fuel nozzle. After time, however, the bolts or holes become worn and the same misalignment problems arise. Further, due to its complexity, this design can be difficult and expensive for retrofit applications.
Consequently, a need still exists for an innovation which will provide a solution to the aforementioned problems in the prior art without introducing any new problems in place thereof.